The present invention relates generally to air pollution control assemblies and particularly to assemblies and methods which control and treat gas streams to remove pollutants. Particularly, the invention relates to an air pollution control assembly for treating acid gas streams from incinerators and the like. More particularly, this invention relates to a synergistic combination of assemblies to effectively treat polluted gas streams, such as a dry scrubber assembly for removing acid gasses.
In the past, various air pollution control apparatus and methods have been proposed and utilized in treating various flue gas streams. For example, Applicant""s U.S. Pat. Nos. 3,876,402, 3,877,899, 4,105,421, 4,113,449 and 4,158,554 disclose apparatus and methods used to filter particulate laden gases. Fabric filtration structures and methods are generally disclosed directing particulate laden gas streams into baghouses. Structures and methods are also disclosed for cleaning filter bags of a baghouse as well as structures arranged to permit filtering elements to be replaced as a unit. These patents provide a background showing air pollution control equipment designs and methods.
Air pollution and environmental quality concerns continue to increase controls on industrial emissions via various laws, statutes, and mandates by regulatory agencies. The separation of undesirable particulate matter from effluent streams by fabric filtration is a method of controlling air pollution. Fabric filtration is performed using dust collection apparatus or baghouses which operate, except for scale, on the principle of vacuum cleaners. A baghouse is typically a sheet metal housing divided into two chambers, or plenums, by one or more tube sheets. Disposed within openings communicating with the plenums are fabric filters. A particle-laden gas stream, induced by a fan, for example, enters one chamber (dirty-air plenum) wherein dust accumulates on the fabric filter as the gas passes through the fabric into the other chamber (clean-air plenum) and out the exhaust. Although baghouses are typically designed in accordance with these principles, there are operational and structural differences between them. The present invention relates to a baghouse wherein the dirty and clean air plenums are separated by a tube sheet having a plurality of vertically suspended filter bags in which cylindrical wire cages are inserted for skeletal support. The gas is filtered as it moves from the outside of the bags to the inside. As a result, baghouses constructed in this manner are normally referred to as outside bag collectors and these outside bag collectors are used in the dry scrubber assembly of the present invention.
It has been found desirable and necessary to precondition and treat gas streams prior to filtration. For example, flue gas streams with acid gases may damage and reduce the effectiveness of equipment and the acid gases are preferably removed or treated in the gas stream prior to and during filtration. By law, current codes require high efficiency removal of acid gases. One object of the present invention is to comply with environmental laws to remove acid gases, such as HCl and SO2, from flue gas streams prior to and during filtration, specifically as in the dry scrubber assembly of the invention.
As further discussed herein, a dry scrubber assembly utilizes the filter or dust cake that forms on the bags used during filtration. A filter or dust cake is the concentrated solid or semisolid material separated from the gas stream and which remains on the filter surface after filtration. The dry scrubber assembly of the present invention uses known cleaning methods to clean the filter cake from the filter bags in a partial and controlled manner. One such known and common method to remove dust cake from the bags is to pneumatically flex the bag with a quick, jet blast of air known as pulse jet bag cleaning and which is used to control the filter cake thickness. The method particularly relates to this invention and is accomplished by delivering a burst of compressed air into a venturi throat located in the clean-air plenum which directs the burst of air into the mouth of the bag, causing the bag to flex outwardly and dislodge the dust cake. In operation, the bags are cleaned in rows on a pre-selected cleaning cycle. The dislodged cake falls into the hopper and is removed from the baghouse by a screw conveyor.
The control of the filter cake thickness essentially controls the effectiveness of active reagent. Another object of the invention is to provide a baghouse cleaning method and to control the filter cake accumulated on the bag surfaces. The filter cake management system of the invention controls the filter cake on the bag surfaces to effectively deal with any acid gases remaining in the flue gas stream.
The present invention provides an air pollution control assembly and method which relates to the treatment and removal of pollutants from gas streams. Specifically, the invention relates to an air pollution control assembly to treat flue gas streams having acid gases and other pollutants. The assembly may comprise an evaporative cooler and/or spray dryer gas distribution system used to treat a gaseous stream to improve the removal of matter in air pollution control equipment. The assembly further provides a reagent injection venturi to treat a gaseous stream having an acidic gas content. The assembly and method also comprises a baghouse assembly and a filter cake management system which enhance the removal of reactive and absorbable pollutants.
The object of this invention is to effectively and efficiently remove pollutants from gas streams, and particularly flue gas streams having acid gases. The evaporative cooler and spray dryer gas stream distribution system, the reagent injection venturi assembly, baghouse assembly and filter cake management system may be individually utilized or may be used in combination with each other depending upon the nature of the flue gas streams to be treated. For example, in one embodiment of the air pollution control assembly the object is to provide a dry scrubber assembly comprising a reagent injection venturi assembly and a baghouse assembly having a filtercake management system.
These and other benefits of this invention will become clear from the following description by reference to the drawings.